Find acidic aquenous solutions

[Jaggis]

Homework Statement

Which of the following chemical compounds are acidic aqueous solutions?

C2H2, C3H8, CH3OH, HCOOH, CH3OCH and benzene.

Homework Equations

Not known.

The Attempt at a Solution

The hydrocarbons aren't polar, that much I know. In the list there are, however, two polar compounds...

I know the answer is that only HCOOH is an acidic aqueous solution, but no explanation is given. Am I supposed to be able to tell which ones are acidic aquenous solutions simply by looking at the chemical formula? Should I write the reaction first ([compound] + H2O → ...) and if so, how would I know what the products are in each case? After all, wouldn't I need the products in order to determine how much H3O- and HO-ions are produced?

 

[Jaggis]

Actually, I also have a second question: which of the above mentioned compunds form hydrogen bonds between molecules? The book gives me the answer but not explanation.

Again, how am I supposed to know this simply by looking at the formulas?

 

[Borek]

It is about functional organic groups and recognizing alcohol, aldehyde and carboxylic acids.